Opiate supplied by Morse, perhaps by means of pill (7)
I believe the answer is:
codeine
'opiate' is the definition.
(thesaurus)
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for codeine that I've seen before include "An anodyne" , "Common painkiller" , "Morphine-derived analgesic; die once (anag.)" , "Analgesic drug" , "Derivative of opium used as an analgesic" .)